The Gateway LT4010u is a netbook. It does not have a Pentium dual core CPU. It has an Intel Atom N2600 CPU in it.
Atom CPUs are soldered into the motherboard. Realistically speaking it would be very difficult and time consuming to de-solder the N2600 which has 559 pins that need to be de-soldered. The only possible upgrade is the Atom N2800 CPU which is 1.86GHz. That CPU would need to be soldered into the motherboard and there is no guarantee that your netbook's BIOS will recognize it. If the BIOS cannot recognize it, the netbook will not boot up. Lastly, these Atom CPUs are not sold to consumers, they are sold directly to laptop builders (OEMs) like Dell and HP.